Lamotrigine (Lamictal®), Serum
| Lamotrigine (Lamictal®), Serum | | | |
| Number | | 716944 |
| CPT | | 82491 |
| Synonyms | | Lamictal® |
| Specimen | | Serum or plasma |
| Volume | | 2 mL |
| Minimum Volume | | 0.6 mL |
| Container | | Red-top tube, lavender-top (EDTA) tube, or green-top (heparin) tube |
| Collection | | Transfer separated serum or plasma to a plastic transport tube. Do not use a gel-barrier tube. The use of gel-barrier tubes is not recommended due to slow absorption of the drug by the gel. Depending on the specimen volume and storage time, the decrease in drug level due to absorption may be clinically significant. |
| Storage Instructions | | Maintain specimen at room temperature. |
| Causes for Rejection | | Gel-barrier tube |
| Reference Interval | | Therapeutic: trough: 2.0-20.0 μg/mL |
| Methodology | | Liquid chromatography/tandem mass spectrometry (LC/MS-MS) |
| Additional Information | | Lamotrigine is an antiepileptic drug (AE) of the phenyltriazine class that is chemically unrelated to existing AEDs. The precise mechanism of action is unknown although it has been postulated that lamotrigine inhibits voltage-sensitive sodium channels thereby stabilizing neuronal membranes and consequently modulating presynaptic transmitter release of excitatory amino acids (eg, glutamate, aspartate). Lamotrigine is 55% bound to plasma proteins and is metabolized predominately to an inactive 2-N-glucuronide conjugate. Peak plasma concentration occurs at 1.4-4.8 hours following oral administration.1 The elimination half-life varies from 12-70 hours. The longer half-lives are observed in patients on concomitant valproic acid therapy. Accordingly, if lamotrigine is co-administered with valproic acid, the dose of lamotrigine must be reduced to less than half the normal dosage. The most common adverse reactions are associated with the use of lamotrigine in combination with other anticonvulsants, and includes dizziness, diplopia, ataxia, blurred vision, nausea and vomiting, somnolence, headache, and rash. The anticonvulsants phenytoin, phenobarbital, primidone, and carbamazepine can reduce lamotrigine levels when co-administered.2 Conversely, lamotrigine can reduce levels of levetiracetam when co-administered.3 In children, investigators4 have found large differences in lamotrigine plasma levels in patients with improvement in seizure frequency, but patients who were seizure-free had higher lamotrigine levels than other patients in the study. |
| Footnotes | | - Lensmeyer GL, Gidal BE, and Wiebe DA, “Optimized High-Performance Liquid Chromatographic Method for Determination of Lamotrigine in Serum With Concomitant Determination of Phenytoin, Carbamazepine, and Carbamazepine Epoxide,” Ther Drug Monit, 1997, 19(3):292-300.
- Bourgeois BF, “Pharmacokinetic Properties of Current Antiepileptic Drugs. What Improvements Are Needed?” Neurology, 2000, 55(Suppl 3):S11-S16.
- May TW, Rambeck B, and Jurgens U, “Serum Concentrations of Levetiracetam in Epileptic Patients: The influence of Dose and Comedication,” Ther Drug Monit, 2003, 25(6):690-9.
- Bartoli A, Guerrini R, Belmonte A, et al, “The Influence of Dosage, Age, and Comedication on Steady State Plasma Lamotrigine Concentrations in Epileptic Children: A Prospective Study With Preliminary Assessment of Correlations With Clinical Response,” Ther Drug Monit, 1997, 19(3):252-60
|
|